The fuel nozzles for gas turbine engine combustors typically include a primary fuel circuit and an independent secondary fuel circuit where the secondary fuel circuit is actuated solely during high power engine operation. As is well known the secondary circuit may include its own fuel nozzle or may be included in the fuel nozzle that incorporates the primary circuit.
In the latter configuration, the secondary fuel circuit has been a single orifice concentric with the primary circuit orifice and coaxial with the axis of the tip of the fuel nozzle. Other fuel nozzle configurations include multiple orifices concentrically and symmetrically spaced about the axis of the nozzle tip referred to the industry as radial jets.
Generally, the high power fuel flow enters the burner through the secondary circuit, which typically produces a fuel distribution symmetric about the coincident axes of the air swirler and the fuel nozzle tip. In all of these secondary fuel circuits, it is necessary to achieve fuel spray penetration into the swirling air produced by the fuel nozzle's air swirlers and to prevent swirler-air-induced collapse of the fuel spray. The multiple secondary fuel orifices (radial jets) were an improvement over the single secondary fuel orifice inasmuch as it improved on these requirements. Both the single orifice and radial jet configurations for the secondary fuel, circuit, as mentioned above, produce a fuel distribution just downstream of the fuel nozzle's air swirler in the form of a symmetrical spray.
For a combustor to be efficient and effective the combusted gas medium must exhibit a desirable pattern factor prior to delivering the combusted gas medium to the engine's turbine. Heretofore, one of the methods of reducing pattern factor was to incorporate dilution air holes in the combustor to mix additional air with the products of combustion. Because of the increasing amount of air being admitted into the combustor through the front end, the ability to use the dilution zone air jets to effectuate the pattern factor is diminishing. The problem is exacerbated with advanced gas turbine combustors because of the increased combustor size and airflow.
I have found that I can improve pattern factor for the advanced gas turbine engines by employing radial jets in a judicious manner to tailor fuel distribution during high power so as to lower combustor pattern factor without adversely affecting the spray penetration and the ability to prevent swirler-air-induced collapse of the fuel spray. This invention contemplates locating the radial jets in an asymmetrical pattern to produce fuel spray that is tailored to produce a desired temperature distribution at the end of the combustor just upstream of the turbine inlet.